Already known from document FR 2 771 686 is a back comprising:                a structure comprising at least one socket,        a headrest comprising at least one stem mounted so as to slide in said socket between a high position and a low position,        a support connected to the structure,        a slide linked to the stem and capable of sliding relative to the support in a direction of sliding,        a return element interposed between the slide and the support and biasing the headrest to its low position,        a lock having an active state in which it is capable of holding the headrest in the high position and an inactive position in which it releases the headrest.        
Therefore, the headrest may be easily retracted by bringing it to a low position by acting on the lock, in order to prevent it hampering the rear vision of the driver.